The Hindu Business Line : Keeping the air-conditioner cool and running

Of the various problems in a car air-conditioner, one of the most common is the accumulation of dust and debris in the radiator fins and condensing coils.

RIDING OUT the summer heat

There are few things that are more frustrating than switching on the car's air-conditioner on a hot summer day only to find that instead of a blast of cool air a blistering draft hits you.

The soaring temperatures in most parts of the country put car air-conditioners to the ultimate test. While they are built to withstand extreme conditions, a few, simple flaws or problems can cause breakdowns and under-performance. Many of these can be recognised early and rectified before the air-conditioner blows out or, worse, starts heating up the vehicle's interiors during summer.

But to be able to get the best performance from the car air-conditioner and for easier troubleshooting, we have to first understand how it works.

Air-conditioners are relatively simple equipment compared to the many other complex components of a car. So, it is usually much easier to locate the source of a malfunction.

Just like room air-conditioners, the car air-con too works on the same principle of transferring heat from the inside to the outside. The car air-conditioner consists of five functional components — the compressor, the refrigerant gas (usually Freon or R-134), the expansion valve, the condenser and the evaporator.

The heart of the air-conditioner is the compressor, which contains the refrigerant gas. A belt-driven pump, which draws power from the engine, drives the compressor. The compressor's job is to compress the refrigerant and route it to the condensing coils located next to the radiator of the car.

Here, the pressurised gas gives away heat and cools down further even as it is under steady pressure. The whole process leads to the conversion of the refrigerant gas into a liquid that is constantly trying to give away more heat.

The next stage of the cycle starts when the liquefied refrigerant gets directed into the evaporator after it is passed through the expansion valve. On the way, at the expansion valve, the gas suddenly gets into a low-pressure situation (hence the name) and starts evaporating back into its gaseous form. This re-conversion of the liquid into gas leads to a massive drop in temperature inside the evaporator.

A fan blower is then employed to pick up the low temperature from the evaporator and deliver cool air into the car's interiors. Air is blown through the cold evaporator and the cold air is then directed into the car through the dashboard vents.

The evaporated refrigerant gas gets re-routed to the compressor. The cycle then continues until the interior of the car is cooled to the required level. This leads to the thermostat tripping and shutting off the compressor temporarily.

Another component that steps in to help the air-conditioning process is the large fan or blower that dissipates heat from the radiator. Some of today's cars come with two fans — one for the radiator that carries the engine coolant and the other for venting heat coming off the air-conditioner's condenser coils.

Common problems

Of the various problems in a car air-conditioner, one of the most common is the accumulation of dust and debris in the radiator fins and condensing coils.

This leads to a drop in the heat dissipation efficiency of the coils. In turn, the cooling performance is affected, and an overload for the compressor could eventually (since the compressor draws power from the engine) lower engine's power and fuel efficiency.

The simple solution to this problem is a regular pressurised water wash of the radiator and coils. At times, the air-conditioner performance also drops during long trips when the evaporator fins get clogged with ice and frost created from moisture in the air.

The remedy is to move the temperature setting to a slightly higher level along the thermostat dial to get even cooling during a long drive.

A more serious problem that will lead to a drop in air-conditioner performance is leakage of refrigerant gas.

Check the joints and seals in the condenser and evaporator for possible leaks. The solution to this problem, which may be a bit difficult to detect, is getting the refrigerant gas topped up after sealing the leaking spot.

Finally, for more complicated electrical and mechanical problems, it may be sensible to take the car to an authorised mechanic for professional advice.